The present invention generally relates to an amplifier reciprocally connecting a digital amplifier having a pulse width modulation switching system with an analog amplifier, more specifically, to a digital power amplifier converting an inputted analog signal into a digital signal having a regular width by comparing the analog signal with a triangular wave, delaying the digital signal by the use of a logic gate to turn on/off output transistors using the delayed signal, and making the signal operated by the output transistors pass an LC low band pass filter to reproduce the analog signal.
It has been emphasized that linearity of sound amplifiers is more important than efficiency. Therefore, linear amplifiers (analog amplifiers) are the main current of the market by the trend of the times and deficiency in technologies, without considering power consumption much. Until now, analog amplifiers having excellent linearity, ranked A, B, and AB, have been adopted for sound amplifiers. However, when implementing these types of amplifiers as large output amplifiers, it may increase the size of the amplifiers because heatproof plates and cooling fans are essential due to a temperature increase when other energies except the outputted energy are converted into heat, causing great amount of power loss.
On the other hand, in the case of a Push-Pull B amplifier adopted to improve the above problems, it combines two transistors as emitter-floor type to reduce energy loss, thereby obtaining relatively high efficiency, however crossover distortion may occur in levels having smaller signals. The B amplifier can improve crossover distortion caused by small signals to some extent by applying an appropriate sub-feedback, however it cannot completely solve the deterioration of harmonic distortion rates when flowing a high-voltage large current. Because two transistors of the B amplifier are turned on/off in turns, thus it is easy to turn on/off when a small amount of current flows, but it is difficult to quickly turn on/off when a large amount of current flows. That is, it is difficult to quickly turn on/off in a large current area because a bias current does not flow in the B amplifier at all in normal times, thereby deteriorating harmonic distortion rates.
Portions of current flow in the AB amplifier, which is an intermediate type of the A and the B amplifiers, even there is no signal. The size of the current is much smaller than that of the A amplifier, and far bigger than that of the B amplifier. Therefore, the more bias current flows, the more characteristics become close to the A amplifier, on the contrary, the less the bias current flows, the more characteristics become close to the B amplifier.
An analog amplifier has various structures according to configuration, and here, the B amplifier is described in FIG. 1.
The B amplifier described in FIG. 1 has approximately 75% efficiency, emitting approximately 25% loss as heat. And, analog signals are inputted to output transistors (QA, QB), causing the output transistors to keep operating, thus lowering efficiency of the output transistors, and requiring a heatproof plate and a cooling fan. As a result, the size of the amplifier gets bigger owing to the heatproof plate and the cooling fan, causing a noise. The life span of the amplifier can be shortened due to a temperature increase. However, the biggest problem is that efficiency of the amplifier gets deteriorated.
To solve the above problems, it is an object of the present invention to provide a digital power amplifier applying digital signals to output transistors to output the digital signals, in order to prevent efficiency deterioration of the output transistors as well as preventing the size of the transistors from increasing due to a constant signal applied to the output transistors, thereby improving efficiency of the output transistors.
To achieve the above object, the present invention provides a digital amplifier comprising an amplifier amplifying inputted analog signals; a triangular wave oscillator generating a triangular wave having a regular frequency; a comparator comparing output signals of the amplifier with output signals of the triangular wave oscillator to output a square wave; a switching block composed of a first switch and a second switch and switching the first switch and the second switch in turns by output signals of the comparator; a controller preventing the first switch and the second switch of the switching block from being in the same state at the same time; a filter performing a filtering according to output signals of the switching block controlled by the controller; and a sub-feedback circuit performing a sub-feedback operation for output signals of the filter to input the sub-fed signals to the amplifier.
Also, the digital power amplifier comprises a first amplifier block including a non-inverting amplifier performing a non-inverting amplification for inputted analog signals; a triangular wave oscillator generating a triangular wave having a regular frequency; a first comparator comparing output signals of the amplifier with output signals of the triangular wave oscillator to output a square wave; a first switching block composed of a first switch and a second switch and switching the first switch and the second switch in turns by output signals of the first comparator; a first controller preventing the first switch and the second switch of the switching block from being in the same state at the same time; a first filter performing a filtering according to output signals of the first switching block controlled by the controller; and a first sub-feedback circuit performing a sub-feedback operation for output signals of the first filter and inputting the sub-fed signals to the amplifier.
The digital power amplifier comprises a second amplifier block including an inverting amplifier inputting inverted analog signals and inputting a regular voltage to amplify the analog signals; a second comparator comparing output signals of the inverting amplifier with output signals of the triangular wave oscillator to output a square wave; a second switching block composed of a third switch and a fourth switch and switching the third switch and the fourth switch in turns by output signals of the second comparator; a second controller preventing the first switch and the second switch of the switching block from being in the same state at the same time; a second filter performing a filtering according to output signals of the second switching block controlled by the second controller; and a second sub-feedback circuit performing a sub-feedback operation for output signals of the second filter and inputting the sub-fed signals to the inverting amplifier. The first amplifier block and the second amplifier block are symmetrical to each other based on load.